This heinous and misused phrase gets tossed around quite a bit by blood bankers. What we mean is this: When we have patients with warm autoantibodies, it is often impossible to find units of red cells that are compatible in the crossmatch test. As a result, we may have to choose to give a product that is incompatible by crossmatch. When we do this, it is most common for the blood bank staff to test the patient’s serum/plasma against multiple different units, and choose the one that shows the least amount of incompatibility (therefore, is “least incompatible” with the donor). The problem is not only that the phrase is awkward (why on earth isn’t it “most compatible?”), but also that it doesn’t mean anything! There is no evidence that choosing units that react less with an autoantibody improves survival of those transfused red cells at all! Sorry for the rant, but this one bugs me a little bit!
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